The present invention concerns a robot arm with associated torque compensation for at least one motional degree of freedom.
Robots having pivotable arms are used in the automobile industry for welding the chassis. The bearing of this type of arm is normally unstable and measures must taken to prevent the arm from tilting over downwardly about the pivot axis. Various methods are used in order to prevent this.
Brakes can be provided to prevent tipping. For example, a brake disposed on a driven linkage having a rotational degree of freedom is disclosed in EP-0093889 A1. This conventional configuration has a gear ring disposed on a braking solenoid which can engage a gear ring disposed on a rotor of an electrical motor drive to prevent rotation of the linkage.
For maintenance and when moving the robot out of its neutral equilibrium position, a stable neutral position must be guaranteed when the brake is released without the danger of tilting over. This requires additional structures for torque compensation.
Prior art has used counter weights which directly or indirectly act on the pivot axis via a linkage. Except for the required checks of the linkage, this configuration is essentially maintenance-free. However, the inertia of the arm is thereby increased, which makes the drive more difficult and expensive to construct.
Conventional mechanical spring elements are relatively maintenance-free. However, they require a large amount of space and do not facilitate pivot-dependent or otherwise adjustable compensation.
Hydraulic or pneumatic cylinder-piston configurations for torque compensation are also known in the art. One end of the cylinder-piston configuration is eccentrically linked to a component rotating along with the pivot axis, whereas the oppositely lying end is linked to a fixed base member of the robot arm. The application of pressure to the piston exercises force from the base onto the eccentric to prevent a tipping over of the arm. These types of cylinder-piston configurations can produce an amount of force which is necessary to prevent tilting and are also compact. Regulation of the pressure in the cylinder permits these forces to be adjusted. Cylinder-piston configurations are however relatively maintenance intensive and therefore rather expensive to use. In addition, pneumatic cylinders require a separate air connection and hydraulic cylinders have problems with regard to leakage.
Alternatively, the drive motor moving the robot arm about the pivot axis can provide the required opposing torque. However, this is only practical for small forces, since a substantial increase in effort with regard to the motor, the linkage, and the associated servo amplifiers is otherwise required.
It is therefore the purpose of the invention to avoid the above mentioned disadvantages while guaranteeing an improved torque compensation, in particular, of simpler construction and reduced maintenance.